The present invention relates to automatic registration of color television cameras, and more particularly to a system for controlling calibration and sensitivity in such automatic registration systems.
Color television cameras currently in use employ two or more image pick-up devices upon which the same scene is simultaneously focused. The occurrence of the video signals produced by these image pick-up devices must be synchronized so as to simultaneously convey information relating to the same portion of the focused image. This registration of the color video signals is generally accomplished by means of a registration circuit which detects errors in registration and automatically supplies control signals to readjust the registration accordingly.
These automatic registration circuits operate by detecting the occurrence of transitions in each of the video signals. Since the transitions correspond to transitions in brightness in the picture being imaged, similar transitions should occur simultaneously in all of the video signals. The registration control circuit supplies control signals which will cause corresponding transitions in the different video signals to occur simultaneously. The correct operation of these circuits is thus dependant upon the existance of such transitions (corresponding to detail in the picture being imaged) in the video signals. If the picture being imaged lacks sufficient picture detail, the automatic registration signal may wander from the correct setting; this may cause a complete loss of registration. In the past, manually operable switches have been provided which would be actuated by the camera operator to disable the operation of the automatic registration circuit when sufficient picture detail was lacking.
Automatic registration circuits are often designed to operate in a cyclical fashion, providing registration control of first one and then another of the color video signals in successive operating cycles. An operating cycle may also be included for automatically calibrating the operation of the registration control circuit, thereby preventing incorrect registration adjustment as a result of component variations, component aging, thermal effects, etc. Systems of this nature are disclosed in the patent to Dischert et al, U.S. Pat. No. 3,830,959 and the Monahan United States application Ser. No. 643,169, filed on Dec. 22, 1975, now U.S. Pat. No. 4,053,203. Since the registration system will not operate properly unless the system has been calibrated, it would be desirable to instead provide a system wherein calibration is automatically monitored and fully adjusted before registration of the video signals may proceed.
The present invention provides an automatic registration system which includes a sensitivity control for disabling the operation of the registration circuit automatically when insufficient picture detail exists. The system also includes means for determining when the system is not in calibration, and for locking the system in the calibration mode until calibration has been achieved.
In accordance with the present invention, a control circuit is provided for use in an automatic registration system which functions in cycles of operation and which provides registration control signals at the conclusion of each cycle of operation. A picture detail circuit is provided for determining the amount of picture detail existing during each cycle of operation and for enabling or disabling the response of the system to the registration control signal generated in that cycle of operation in accordance therewith. A calibration control circuit is provided for determining when a calibration error exists and for forcing the registration system to provide successive calibration cycles of operation until calibration has been achieved.